704 THE POPULAR SCIENCE MONTHLY. 



person who believes that he tastes poison in his food when he imaoines 

 that some one wishes to poison him, or sees an enemy lurking about 

 his premises when he believes himself to be the victim of perse- 

 cution. 



Here, then, we are brought to one efficient cause of hallucinations 

 namely, a vividly -conceived idea which is so intense that it appears 

 to be an actual perception, a mental image so vivid that it becomes a 

 visual image. Everybody knows that the idea or imagination of a 

 sensation will sometimes cause a person to feel the sensation ; the 

 mention or the sight of certain little insects which inhabit the bodies 

 of uncleanly persons seldom fails to make the skin itch uncomfortably. 

 John Hunter said of himself, " I am confident that I can fix my atten- 

 tion to any part until I have a sensation in that part." Sir Isaac 

 Newton could call up a spectrum of the sun when he was in the dark, 

 by intense direction of his mind to the idea of it, " as when a man 

 looks earnestly to see a thing which is difficult to be seen." Dickens 

 used to allege that he sometimes heard the characters of his novels 

 actually speak to him ; and a great French novelist declared that, when 

 he wrote the description of the poisoning of one of his characters, he 

 had the taste of arsenic so distinctly in his mouth that he was himself 

 poisoned, had a severe attack of indigestion, and vomited all his din- 

 ner a most pregnant proof of the power of imagination over sense, 

 because arsenic has scarcely an appreciable taste beyond being sweet- 

 ish ! Artists sometimes have, in an intense form, the faculty of such 

 vivid mental representation as to become mental presentation. It was 

 very notable in that extraordinary genius, William Blake, poet and 

 painter, who used constantly to see his conceptions as actual images or 

 visions. " You have only," he said, " to work up imagination to the 

 state of vision, and the thing is done." The power is, without doubt, 

 consistent with perfect sanity of mind, although it may be doubtful 

 whether a person who thought it right for himself and his wife to imi- 

 tate the naked innocence of paradise in the back-garden of a Lambeth 

 house, as Blake did, was quite sane ; but too frequent exercise of the 

 power is full of peril to the mind's stability. A person may call up 

 images in this way, and they will come, but he may not be able to dis- 

 miss them, and they may haunt him when he would gladly be rid of 

 them. He is like the sorcerer who has called spirits from the vasty 

 deep, and has forgotten the spell by which to lay them again. Dr. 

 Wigan tells of a skillful painter whom he knew, who assured him that 

 he had once painted three hundred portraits in one year. The secret 

 of his rapidity and success was, that he required but one sitting and 

 painted with wonderful facility. " When a sitter came," he said, " I 

 looked at him attentively for half an hour, sketching from time to time 

 on the canvas. I wanted no more ; I put away my canvas and took 

 another sitter. When I wished to resume my first portrait, I took the 

 man and set him in the chair, where I saw him as distinctly as if he had 



